1. Field of the Invention
The present invention relates to a method for controlling the operating temperature of a catalytic reactor. While this is applicable to different types of catalytic reforming reactors, it is described here with reference to a Catalytic Partial Oxidation Reactor since the constraints of high temperature and coking are most acute. The present invention provides a method for protecting the catalyst from temperature excursions, minimizing coking, compensating for suboptimal mixing at the feed, recovering from operation under coking regimes, and providing for a much longer run-time duration at maximum operating temperature, and periodically or actively maintaining the minimum operating temperature.
2. Brief Description of the Related Art
There are many methods known in the art for controlling the operating temperature of a chemical reactor. Closed-loop systems are among these known methods. Typically, a controller is employed such that one or more output variables of a system are tracked against a certain reference points over time. The controller varies the inputs to a system to obtain the desired effect on the output of the system thereby maintaining the output variables at or near the reference points. Accordingly, a closed-loop system for controlling the operating temperature of a chemical reactor would monitor the reactant products or other operating parameters such as operating temperatures, track the measurements and compare such values to a desired reference. The system would provide for varying the reactor input and other operating parameters in order to maintain the operating temperature of the reactor at or near a reference point or reactor temperature setpoint.
Waterless catalytic partial oxidation (hereinafter referred to as “CPOx”) of liquid distillate fuels, such as, for example, diesel and JP8, with near complete conversion to Carbon (C1) products is a challenging proposition. The general reaction is shown below:CxHy+O2→mCO+nH2+small amounts of CO2 and H2OThe practical ability to operate in this mode requires a reactor design that provides high selectivity to the partial oxidation products CO and H2 compared to the complete oxidation products CO2 and H2O. While some studies have described CPOx of diesel, typically these have not been operated in “dry” mode (i.e., the reactions have been performed by adding some steam from an external source, or by partially burning some of the hydrocarbon feed to generate water in-situ, and/or by using an upstream process to remove the heavier ends from the fuel).
Moreover, CPOx of distillate fuel is made difficult due to carbon formation and/or excessively high reactor temperatures. In the present invention, in conjunction with reactor design, unique control algorithms permit operational precision that addresses the constraints of dry CPOx. Thermodynamic considerations of dry CPOx, as well as the hurdles and design requirements identified to develop a dry CPOx reactor, also must be considered and explained here.
Due to the thermodynamic drive for coke formation, which can be exacerbated by inherent non-uniformities in the feed to a CPOx reactor, there is a need to diminish this coke formation and the subsequent catalyst temperature spread resulting from increasing flow disparities that arise. By limiting fuel flow over a certain span, the maximum operating temperature of a reactor can serve as a measured process variable and subsequently controlled in closed-loop fashion. However, under coking and/or suboptimal mixing/fuel-atomization/vaporization conditions, having a maximum operating temperature within the reactor (hereinafter “Tmax”) set such that the minimum operating temperature within the reactor (hereinafter, “Tmin”) is above the thermodynamic threshold for coking will only be useful for a short time; inherent cold zones may develop, dropping the Tmin even though Tmax is held constant. In this case, attempting to increase Tmin at point in the reactor by adjusting the fuel input would have the undesirable effect of increasing Tmax at another point in the reactor. Therefore, a periodic need for a second closed-loop system controlling air or other means to increase the Tmin is desirable.
It is an object of the present invention to provide a method for controlling the operating temperature of a reactor using a closed-loop system that provides for varying the reactor input and other operating parameters in order to maintain the operating temperature of the reactor at or near the initial setpoint temperature for operation of the reactor. It is another object of the present invention to provide a method for controlling the operating temperature of a reactor using a closed-loop system that provides for controlling the operating temperature of a CPOx reactor which maintains temperatures within the catalytic reactor below material limits but above threshold temperatures for coking.